There are a variety of detectors that rely upon ionization. For example, ionization is used to ionize gas molecules for detecting the presence of a particular gas or substance.
There are well known ionization sources including Ni63 and Americium 241. Both of these are radioactive. Ni63 is used in ion mobility spectrometry (IMS) and field asymmetric ion mobility (FAIMS) detectors and other applications where high energy, high flux ionization is required. FAIMS, for example, is highly sensitive and selective for toxic and combustible gas detection. Americium 241 is used in smoke detectors, for example.
The ionization in a detector will ionize air or another gas within a test chamber. The test chamber typically has a metal plate that is maintained at a positive voltage. Molecules within the chamber that have been ionized are accelerated toward the plate. A portion of the ions collide with a collector electrode located between the ionization source and the plate. Ions that collide with the plate generate a current and ions that collide with the collector electrode also generate a current. The ratio of these currents is compared to determine whether a substance of interest is present.
One drawback associated with known detectors is that they include a radioactive material within the ionization source. Another drawback is that the source of radioactive particles does not provide a consistent or tunable energy level.
One suggestion for avoiding radioactive materials within an ionization source is to use soft x-rays for ionization. One such example arrangement is shown in the United States Patent Application Publication No. U.S. 2010/0032560.
One challenge associated with using an x-ray or electron source for ionization is that it requires a vacuum within an enclosed chamber to sufficiently accelerate the electrons from an electron emission source. Given that many ionization devices utilize very small components, it is difficult to establish a window that allows electrons or x-rays to pass and that is mechanically strong enough to withstand the pressure differential across the window.